1. Field of the Invention
The present invention relates to image forming apparatuses, such as a laser printer, a laser copying machine and other apparatuses capable of forming images, and an optical scanning apparatus used in such image forming apparatuses.
2. Discussion of Related art
An optical scanning apparatus used in image forming apparatuses such as a laser printer and a laser copying machine scans a surface of a photoconductor, which functions as a surface to be scanned, using light emitted from a light source to optically form information and images on the surface to be scanned.
An optical scanning apparatus described in Japanese Laid-open Patent Publication No. 9-211944 includes more than two laser diodes as light emitting devices of a light source. When any one of the laser diodes are broken and if at least one of the laser diodes is functioning normally, the apparatus optically forms information on a photoconductor, which defines a surface to be scanned, by using the laser diodes functioning normally while reducing the rotation speed of the photoconductor in accordance with the number of the laser diodes which are functioning normally.
Japanese Laid-open Patent Publication No. 10-151798 describes another optical scanning apparatus, in which a photoconductor is optically scanned with beams emitted by a plurality of light emitting devices. When a light detector detecting the light emitting conditions of the light emitting devices detects that any one of the light emitting devices is not operating properly and is no longer emitting light such that the optical image forming performance of the light emitting devices has been decreased, the apparatus optically forms information and images using the light emitting devices which are functioning normally while adjusting the relative moving speed of the photoconductor and the scanning beams according to the number of light emitting devices which are defective and are no longer emitting light. More specifically, the apparatus reduces the moving speed of the photoconductor according to the number of light emitting devices which are defective and are no longer emitting light.
As described above, in conventional devices, when any of a plurality of light emitting devices of a light source are broken, in order to form an image having substantially the same quality as that of the images formed when the plurality of light emitting devices are functioning normally, a method to reduce a moving speed of a surface to be scanned is used. However, this method has a problem in that the moving speed of the scanned medium is significantly decreased and thereby, the image forming performance of the apparatus is greatly decreased.
In order to overcome the above-described and other problems, preferred embodiments of the present invention provide a novel optical scanning apparatus that forms images having substantially the same quality as the quality of the images formed when all of a plurality of light emitting devices of a light source of the optical scanning apparatus are functioning normally even when any one of the plurality of light emitting devices are damaged or broken, without decreasing the image forming performance of the apparatus, by detecting one or more damaged or broken light emitting devices and then compensating for the light omitted due to the damaged or broken light emitting devices using the normally functioning light emitting devices without decreasing the image forming speed of the optical scanning apparatus.
According to a preferred embodiment of the present invention, a novel apparatus and method of detecting a defective or broken light emitting device in an optical scanning apparatus includes arranging a light receiving element along an optical path including a synchronous detecting sensor, an imaging element and a mirror. The light receiving element can be located between the synchronous detecting sensor and the imaging element, or between the imaging element and the mirror. The light receiving element preferably has an opening having a shape which produces different light intensity at different points along the synchronous detecting sensor so that the synchronous detecting sensor can detect the difference between actual light passing through the light receiving element in the form of the light sensed at the synchronous detecting sensor and the expected light intensity distribution when all light emitting devices are operating normally. A defective light emitting device is detected by determining differences between actual and expected values for light intensity and light volume. Once a defective light emitting device is detected, a controller identifies which light emitting device is defective and makes a correction that is appropriate to correct for the defective light emitting device.
Other preferred embodiments of the present invention provide various novel apparatuses and methods for compensating for light omitted due to the damaged or broken light emitting devices using the normally functioning light emitting devices without decreasing the image formation speed of the image forming apparatus. Such novel apparatuses and methods use various solutions such as increasing the rotating speed of the deflector while increasing the modulation speed of the light emitting devices by the same amount, increasing beam spot diameter in the subscanning direction, changing the output power of the light emitting devices on a surface to be scanned in order to increase beam spot diameter in the main scanning direction and the subscanning direction, and changing the focal length of the line image forming optical apparatus and increasing either the rotation speed of the deflector or the rotation speed of the surface to be scanned or photoconductive drum.
According to one such preferred embodiment of the present invention, a novel apparatus and method for optical scanning is such that images are formed to have excellent quality even if one or more of light emitting devices of a light source are damaged or broken, without affecting or decreasing the image forming performance of the apparatus, by compensating for light omitted due to the damaged or broken light emitting devices using the normally functioning light emitting devices and by controlling the deflecting speed of a deflector and the moving speed of a scanned medium.
The preferred embodiments of the present invention further provide a novel optical scanning apparatus that forms images having no white spots caused by omitted light resulting from damaged or broken light emitting devices even when any one of a plurality of light emitting devices of the apparatus are damaged or broken, without deteriorating the image forming performance of the apparatus, by changing the diameter of a beam spot, or the diameter of a dot forming an image, which is formed on a surface of the medium scanned by the beam spot.
According to another preferred embodiment of the present invention, an optical scanning apparatus for scanning a surface with light to optically form information and images on the surface, includes a light source unit having a plurality of light sources which are arranged in a sub-scanning direction such that beam spots are formed at a desired interval on the scanned surface. A coupling lens couples divergent light flux from the light source to a subsequent optical system and a deflector having a deflecting surface deflects incident light flux. A first image forming lens system having a power in a sub-scanning direction forms a line image near a deflecting surface of the deflector and a second image forming lens system forms the light flux deflected by the deflector into an optical beam spot on the scanned surface.
According to preferred embodiments of the present invention, in the above-described optical scanning apparatus, when any one of the plurality of light sources of the light source unit are damaged or broken and if at least one of the plurality of light sources is emitting light normally, a controller controls the apparatus to optically form information on the scanned surface using the light sources that are not damaged and that are emitting light normally.
According to another preferred embodiment of the present invention, in the above-described optical scanning apparatus, when any one of the plurality of light sources of the light source unit are damaged or broken and if at least one of the plurality of light sources is emitting light normally, the apparatus selects light sources from the light sources which are not damaged and are still emitting light normally according to the number of the light sources emitting light normally and the position of the normally emitting light sources in the light source unit and optically forms information on the scanned surface with the selected light sources.
According to various preferred embodiments of the present invention, the apparatus may further include a mechanism to change the position of the first image forming lens system.
According to other preferred embodiments of the present invention, further, the apparatus may change a quantity of light on the scanned surface so as to change a size of a beam spot on the scanned surface when forming information and images on the scanned surface.
Further, according to other preferred embodiments of the present invention, the diameter of a beam spot scanning the scanned surface may be made larger than a size relative to a resolution of dots formed by the beam spot on the scanned surface.
According to another preferred embodiment of the present invention, in the above optical scanning apparatus, when any one of the plurality of light sources are damaged or broken and if at least one of the plurality of light sources is emitting light normally, a deflecting speed of the deflector is changed according to the number of light sources that are not damaged and are still emitting light normally and according to the position of the normally emitting light sources in the light source unit.
According to still another preferred embodiment of the present invention, in the above optical scanning apparatus, the apparatus further preferably includes a plurality of openings or apertures and a switching device to switch the plurality of openings or apertures which are constructed to change the diameter of the opening among a plurality of diameters, and, when any one of the plurality of light sources are damaged or broken and if at least one of the plurality of light sources is emitting light normally, one of the plurality of openings is arbitrarily selected or one of the plurality of diameters of the openings is selected according to the number of light sources that are not damaged and are still emitting light normally and the arrangement of the normally emitting light sources in the light source unit so as to regulate light flux from the light source with the selected one of the plurality of openings or the opening having the selected diameter.
According to still another preferred embodiment of the present invention, the above-described optical scanning apparatus includes a plurality of first image forming lens systems having a power in a sub-scanning direction and forming a line image near a deflecting surface of a deflector, and when any one of the plurality of light sources are damaged or broken and if at least one of the plurality of light sources is emitting light normally, one of the plurality of first image forming lens systems is selected according to the number of the light sources that are not defective and are still emitting light normally and the position of the normally emitting light sources in the light source.
According to preferred embodiments of the present invention, the deflecting speed of the deflector or the moving speed of the scanned surface may be changed according to the selected first image forming lens system.
A method of detecting a light emitting device of a light source unit, which is not functioning normally, from a plurality of the light emitting devices included in the light source unit, using a light receiving element configured such that the distance that each beam from the plurality of light emitting devices passes over the light receiving element in the main scanning direction is different from each other.
A light receiving element for detecting one or more of a plurality of light emitting devices, of a light source unit, that are not functioning normally, is configured such that the distance that each beam emitting from the plurality of the light emitting devices passes over the light receiving element in the main scanning direction is different from each other. The light receiving element is arranged in the main scanning area of a scanning apparatus after a deflector and outside of an effective main scanning area of the scanning apparatus.
Other features, elements, advantages and characteristics of the present invention will become more apparent from the detailed description of preferred embodiments of the present invention in conjunction with the attached drawings.